Wellbore logging tool assembly

ABSTRACT

A logging tool assembly comprises an elongate sensor assembly, a plurality of sensor transportation apparatuses for transporting the elongate sensor assembly through a wellbore, and an orientation structure. The sensor transportation apparatuses are spaced apart along the elongate sensor assembly. Each sensor transportation apparatus comprises an engagement structure to connect the sensor transportation apparatus to the elongate sensor assembly and prevent relative rotation between the sensor transportation apparatus and the elongate sensor assembly, and one or more pairs of wheels arranged to rotate on an axis of rotation substantially perpendicular to a longitudinal axis of the elongate sensor assembly. The axes of rotation of the pairs of wheels of said transportation apparatuses are parallel. The orientation structure is connected to the elongate sensor assembly to prevent relative rotation between the orientation structure and the elongate sensor assembly. The orientation structure comprises at least one radially extending orientation projection. In a transverse outline of the logging tool assembly a said orientation projection extends between the pair of wheels so that the shortest distance between a centre of gravity of the elongate sensor assembly and the wellbore wall is when the pair of wheels of the transportation apparatus is in contact with the wellbore wall.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-part application of Ser. No. 15/825,074 filed Nov. 28, 2017, which is a Continuation of Ser. No. 14/441,833 filed May 8, 2015, which is a National Stage of International Application No. PCT/NZ2013/000210, filed Nov. 15, 2013, the contents of all of which are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to apparatus and methods for use in transporting sensor equipment, and in particular to apparatus and methods for use in wireline logging applications.

BACKGROUND ART

Hydrocarbon exploration and development activities rely on information derived from sensors which capture data relating to the geological properties of an area under exploration. One approach used to acquire this data is through wireline logging. Wireline logging is typically performed in a wellbore immediately after a new section of hole has been drilled. These wellbores are drilled to a target depth covering a zone of interest, typically between 1000-5000 meters deep. A sensor package, also known as a “logging tool” or “tool-string” is then lowered into the wellbore and descends under gravity to the target depth of the wellbore well. The logging tool is lowered on a wireline—being a collection of electrical communication wires which are sheathed in a steel cable connected to the logging tool. Once the logging tool reaches the target depth it is then drawn back up through the wellbore at a controlled rate of ascent, with the sensors in the logging tool operating to generate and capture geological data.

There is a wide range of logging tools which are designed to measure various physical properties of the rocks and fluids contained within the rocks. The logging tools include transducers and sensors to measure properties such as electrical resistance, gamma-ray density, speed of sound and so forth. The individual logging tools are often combinable and are typically connected together to form a logging tool-string. These instruments are relatively specialised sensors, which in some cases need to be electrically isolated or located remote from metallic objects which are a source of noise in the data generated. Some sensors are designed to make close contact with the borehole wall during data acquisition whilst others are ideally centred in the wellbore for optimal results. These requirements need to be accommodated with any device that is attached to the tool-string.

The drilling of wells and the wireline logging operation is an expensive undertaking. This is primarily due to the capital costs of the drilling equipment and the specialised nature of the wireline logging systems. It is important for these activities to be undertaken and completed as promptly as possible to minimise these costs. Delays in deploying a wireline logging tool are to be avoided wherever possible.

One cause of such delays is the difficulties in lowering wireline logging tools down to the target depth of the wellbore. As the logging tool is lowered by cable down the wellbore by gravity alone, an operator at the top of the well has very little control of the descent of the logging tool. Logging tools can become held up on ledges of rock formed inside a well—usually found at the boundaries of hard rock layers where the adjacent rock layer crumbles. An operator may not immediately identify that a logging tool has become stuck on a ledge, and may also spend a significant amount of time reeling the cable and tool-string back in and attempting to move it past the obstruction formed by a ledge.

The chances of a wireline logging tools getting stuck or being impeded is also significantly increased with deviated wells. Deviated wells do not run straight vertically downwards and instead extend downward at an angle. Multiple deviated wells are usually drilled from a single surface location to allow a large area of interest to be explored. As wireline logging tools are run down a wellbore with a cable under the action of gravity, the tool-string will traverse the low side or bottom of the wellbore wall and immediately encounter any obstructions on the wellbore wall as it travels downwards to the target depth.

Furthermore, in deviated wells there is the potential for drilling cuttings to collect on the low side of the wellbore. Rock cuttings are more difficult to remove when the wellbore is deviated. The logging tool has to travel over or through these drilling cuttings, which can impede its progress and also collect in front of the logging tool. In some cases the logging tool may not be able to plough through the cuttings to reach the bottom of the wellbore.

Furthermore, as hole deviation increases, the sliding friction can prevent the logging tool descending. The practical limit is around 50-60° from the vertical, and in these high angle wells any device that can reduce friction is very valuable. The running of the tool-string over the low side surface of the borehole also needs to be taken into account in the design of the tool-string, and in particular the housing and the containment of its sensitive sensors and transducers.

Attempts have been made to address these issues in the deployment of wireline logging tools, as disclosed in U.S. Pat. Nos. 7,866,384, 7,395,881 and US patent application 20120061098. These patent specifications describe a number of different forms of an in-line roller devices integrated into the logging tool-string. These devices aim to reduce the friction experienced by a tool-string as it is run along the low side slope of a deviated wellbore.

This in-line positioning of roller devices increases the potential to cause damage to the logging tools as there are additional O-rings connections required that could potentially leak.

Furthermore, there are multiple additional electrical connections that need to be made between the individual logging tools making up the logging tool-string. The additional components and tool-string length means it takes longer to connect and disconnect the tool-string, which slows down the wireline logging operation and therefore increases well costs. Further, there is a lack of flexibility inherent in this approach as in-line roller devices can only be placed between logging tools, and as some of these tools are quite long, in-line rollers may not keep the entire tool body off the borehole wall.

The rollers employed in these forms of prior art devices also have relatively small wheels with a minimal clearances. In deviated wellbores well drilling cuttings will collect on the low side of the well, and these small sets of rollers can struggle to make headway through piles of cuttings. In situations where large amounts of cuttings are encountered these small rollers can be of no assistance at all and simply add to the length and weight of an already unwieldy tool.

McNay U.S. Pat. No. 8,011,429 and Schlumberger patent application US2013248208 describe roller assemblies which slip over the logging tool, and are mounted such that they are free to rotate about the longitudinal axis of the tool. These devices have relatively small wheels which do not rotate easily over rough surfaces. In addition, it is often the central or side part of the wheel which is in contact with the wellbore wall, rather than the circumferential or radially extreme edge. This means that the wheels are often skidding rather than rotating. Neither of these devices has an active lubrication system which can prevent contaminants from entering and jamming the bearings.

All of these existing prior art devices attempt to assist a tool-string in travelling down a deviated wellbore. However, the devices do not assist in maintaining a known orientation of the tool-string, or a specific clearance or “standoff” between the active part of the tool-string and the wellbore wall.

U.S. Pat. No. 684,732 describes a sectional threading rod which is provided with wheels to reduce friction as the rod is pushed down a conduit. The wheels have an axle which is above the centre of the rod. However, the rod is not intended for use with a logging tool.

Other attempts to address the issues associated with deviated wellbores include a number of prior art “hole finding” devices. For example U.S. Pat. No. 4,474,235, US patent application US 20120061098, PCT publication WO 2010/106312 and US patent application US20120222857 all describe systems for wireline hole finding devices which rely on one or more rollers located at the nose at the bottom of a tool-string. The nose is the leading end at the bottom of the tool-string during descent of the wellbore. These rollers are arranged to allow the nose of the tool-string to roll into, and then up and over, irregularities and obstructions in a wellbore.

However due to the use of a number of metallic components these types of hole finding devices are not necessarily compatible with induction type resistivity tools which are generally the most commonly used sensor in such applications. Also, some logging tools are “bottom only”, and have sensors which must be located at the lower extremity of the tool-string. The prior art hole finders are heavy and metallic and hence not compatible with such tools.

Furthermore, these systems are relatively complicated and must be appropriately designed and maintained to withstand the hostile environment experienced at depth in exploration wells. If the moving parts used in these systems cease to function the hole finder is ineffective. These designs are also relatively heavy and inflexible. Any impact forces or torque acting on the hole finder are transmitted into the tool-string, potentially causing damage to the sensors.

Another approach used in the design of hole finding devices is disclosed in US patent application US 20090145596. This patent specification describes an alternative hole finding system employed outside of wireline applications where a conduit, tubing or pipe is attached to the sensor tool in order to push it down the wellbore. This specification discloses a relatively complicated system which requires a surface operator to actively adjust the orientation of a nose assembly mounted at the bottom of the tool. The specification also discloses that this device requires a range of sensors that are used to detect sensor tool movement, and specifically if the sensor tool is held up. This form of hole finding system is again relatively heavy and complex. Furthermore, a dedicated operator is also required to monitor the progress of the sensor tool to actively adjust the orientation and angle of attack of the adjustable nose assembly when the sensors detect that the sensor device is held up as it moves down the wellbore. A similar design is described in U.S. Pat. No. 7,757,782. This device is also an active system which requires manipulation from an operator at the surface to change the nose angle and azimuth in order in order to navigate past obstacles after the logging tool is obstructed.

It would be an advantage to have an improved logging tool assembly comprising sensor transportation apparatuses to carry the assembly down a wellbore which addressed any or all of the above issues or at least provided an alternative choice. An improved logging tool assembly with sensor transportation apparatuses and orientation structure which could also be used to orient the logging tool assembly would also be of advantage.

The reference to any prior art in the specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge in any country.

DISCLOSURE OF INVENTION

According to one aspect of the present invention there is provided a logging tool assembly comprising:

-   -   an elongate sensor assembly,     -   a plurality of sensor transportation apparatuses for         transporting the elongate sensor assembly through a wellbore,         the sensor transportation apparatuses spaced apart along the         elongate sensor assembly, wherein each sensor transportation         apparatus comprises:         -   an engagement structure to connect the sensor transportation             apparatus to the elongate sensor assembly and prevent             relative rotation between the sensor transportation             apparatus and the elongate sensor assembly, and         -   one or more pairs of wheels arranged to rotate on an axis of             rotation substantially perpendicular to a longitudinal axis             of the elongate sensor assembly,     -   wherein the axes of rotation of the pairs of wheels of said         transportation apparatuses are parallel, and     -   an orientation structure connected to the elongate sensor         assembly to prevent relative rotation between the orientation         structure and the elongate sensor assembly, the orientation         structure comprising at least one radially extending orientation         projection, in a transverse outline of the logging tool assembly         a said orientation projection extending between the pair of         wheels so that the shortest distance between a centre of gravity         of the elongate sensor assembly and the wellbore wall is when         the logging tool assembly is on the wheels of the transportation         apparatuses.

In some embodiments, there is a single most stable orientation within the wellbore with the logging tool assembly on the wheels of the transportation apparatuses and with the elongate sensor assembly closest to the low side of wellbore wall.

In some embodiments, each wheel has a diameter substantially greater than one of the diameter, width or height of the elongate sensor assembly.

In some embodiments, in a transverse view of the logging tool assembly the elongate sensor assembly is carried between the pair of wheels.

In some embodiments, the elongate sensor assembly comprises a sampling tool oriented to take a sample from a desired side of the wellbore with the logging tool assembly in the stable position.

In some embodiments, the elongate sensor assembly comprises a sampling tool oriented to take a sample from a horizontal side of the wellbore with the logging tool assembly in the stable position.

In some embodiments, the elongate sensor assembly comprises a sampling tool oriented to take a sample from a high-side of the wellbore with the logging tool assembly in the stable position.

In some embodiments, the elongate sensor assembly comprises a sampling tool oriented to take a sample from a low-side of the wellbore with the logging tool assembly in the stable position.

In some embodiments, in the stable position, the axes of rotation of the plurality of sensor transportation devices are above the centre of mass of the elongate sensor assembly with the logging tool assembly in the stable position.

In some embodiments, the axes of rotation of the plurality of sensor transportation devices are on or below the centre of mass of the elongate sensor assembly with the logging tool assembly in the stable position.

In some embodiments, the orientation projection is a bow-spring eccentering device.

In some embodiments, the orientation structure comprises a powered orientation projection moveable between an extended or raised position and a retracted or lowered position.

In some embodiments, lateral extremities of the at least one orientation projection and the bottom of the wheels present lateral extremities of the transverse outline of the logging tool assembly.

In some embodiments, lateral extremities of the at least one orientation projection and the top and bottom of the wheels present lateral extremities of the transverse outline of the logging tool assembly.

In some embodiments, the lateral extremities of the transverse outline of the logging tool assembly have a rotational centre that is offset from the centre of mass of the elongate sensor assembly so that the sensor transportation apparatus is oriented in the most stable position with the centre of mass of the elongate sensor assembly below the rotational centre.

In some embodiments, the pair of wheels are integrally formed as a single wheel providing two spaced apart edges to contact the well bore wall.

According to another aspect of the present invention, there is provided a logging tool assembly comprising:

-   -   an elongate sensor assembly,     -   a plurality of sensor transportation apparatuses for         transporting the elongate sensor assembly through a wellbore,         the sensor transportation apparatuses spaced apart along the         elongate sensor assembly, wherein each sensor transportation         apparatus comprises:         -   an engagement structure to connect the sensor transportation             apparatus to the elongate sensor assembly and prevent             relative rotation between the sensor transportation             apparatus and the elongate sensor assembly, and         -   one or more pairs of skids arranged parallel to a             longitudinal axis of the elongate sensor assembly, and             an orientation structure connected to the elongate sensor             assembly to prevent relative rotation between the             orientation structure and the elongate sensor assembly, the             orientation structure comprising at least one radially             extending orientation projection, in a transverse outline of             the logging tool assembly a said orientation projection             extending between the pair of skids so that the shortest             distance between a centre of gravity of the elongate sensor             assembly and the wellbore wall is when the pair of skids of             the transportation apparatus is in contact with the wellbore             wall

In some embodiment, there is a single most stable orientation within the wellbore with the logging tool assembly on the skids of the transportation apparatuses and with the elongate sensor assembly closest to the low side of wellbore wall.

In some embodiment, lateral extremities of the at least one orientation projection and the skids present lateral extremities of the transverse outline of the logging tool assembly.

According to another aspect of the present invention there is provided a sensor transportation apparatus to convey an elongate sensor assembly through a wellbore, the sensor transportation apparatus comprising:

-   -   at least one engagement structure to connect the sensor         transportation apparatus to the sensor assembly, and     -   one or more wheels arranged to rotate about an axis of rotation         substantially perpendicular to a longitudinal axis of the sensor         assembly when the transportation apparatus is connected to the         sensor assembly, and     -   an orientation structure defining a form having a transverse         outline which has a rotational centre, wherein the rotational         centre is offset from a centroidal axis of the elongate sensor         assembly.

In some embodiments, the lateral extremities of the orientation structure substantially lie on a substantially circular imaginary curve which is centred at the rotational centre.

In some embodiments, the sensor transportation apparatus has only one stable orientation.

In some embodiments, the wheels are shaped and dimensioned such that, in use, contact between each wheel and the wellbore wall is at a surface of the wheel which is at the radial extremity of the wheel, relative to the axis of rotation.

In some embodiments, each said wheel extends below the sensor assembly and the engagement structure when the sensor transportation apparatus is in a substantially horizontal orientation.

In some embodiments, a rotational axis of each said wheel is above the centroidal axis of the tool-string when the sensor transportation apparatus is in a substantially horizontal orientation.

In some embodiments, the rotational axes of the wheels are substantially parallel and coplanar.

In some embodiments, at least two of the wheels have a common axis of rotation.

In some embodiments, the wheels are mounted on stub axles.

In some embodiments, the orientation structure comprises at least one laterally extending orientation projection.

In some embodiments, the orientation structure further comprises at least one of the wheels.

In some embodiments, the wheels run on bearings and the apparatus further comprises a lubrication delivery apparatus which provides a lubricant to the bearings at a pressure which is greater than ambient wellbore pressure.

In some embodiments, the engagement structure engages an exterior surface of the sensor assembly.

In some embodiments, the engagement structure partially encloses the exterior surface of the sensor assembly without completely encircling the sensor assembly.

In some embodiments, a portion of the sensor assembly extends below the engagement structure when the sensor transportation apparatus is in a substantially horizontal orientation.

In some embodiments, the engagement structure is adapted for in-line connection to the sensor assembly.

In some embodiments, the transportation apparatus further comprises a drive means, wherein at least one of the wheels is connectable to the drive means.

In some embodiments, the apparatus further comprises a clutch between the drive means and each driven wheel.

In some embodiments, the apparatus further comprises a jockey wheel mounted to adjustable mounting means for selectively raising or lowering the jockey wheel.

In some embodiments, when the mounting means are raised, the jockey wheel engages an opposite side of the wellbore to the wheels.

According to another aspect of the present invention there is provided a sensor transportation apparatus to convey an elongate sensor assembly through a wellbore, the sensor transportation apparatus comprising

-   -   at least one engagement structure to connect the sensor         transportation apparatus to the sensor assembly, and     -   one or more wheels arranged to rotate on bearings about an axis         of rotation substantially perpendicular to a longitudinal axis         of the sensor assembly when the transportation apparatus is         connected to the sensor assembly, and a lubrication delivery         apparatus which provides a lubricant to at least one of the         bearings at a pressure which is maintained at greater than         ambient wellbore pressure.

In some embodiments, the bearing comprises a ball bearing assembly or a bush bearing assembly.

In some embodiments, the lubrication delivery apparatus comprises a reservoir comprising an elastic diaphragm.

In some embodiments, the reservoir comprises a volume between an inner surface of the reservoir and a base structure.

In some embodiments, the base structure comprises an outer surface of the transportation means.

In some embodiments, an exterior side of the diaphragm is subject to ambient pressure.

In some embodiments, each wheel is mounted to a stub axle.

In some embodiments, the lubrication delivery apparatus comprises a lubrication channel in each said stub axle.

In some embodiments, an outer end of each said stub axle engages a longitudinally extending protection structure.

According to another aspect of the present invention there is provided a sensor transportation apparatus to convey a sensor assembly through a wellbore, the apparatus comprising

-   -   a body to connect to said sensor assembly,     -   one or more wheels arranged to rotate on respective stub axles         about an axis substantially perpendicular to the longitudinal         axis of said sensor assembly when the body is connected to said         sensor assembly,     -   wherein one or more stub axles are supported by an orientation         projection, or wherein one or more wheels are protected by an         orientation projection.

In some embodiments, the orientation projection extends in front of the wheel which is connected to the respective stub axle.

In some embodiments, the orientation projection extends longitudinally to a point behind the wheel which is connected to the respective stub axle.

In some embodiments, the wheel extends above and below the orientation projection.

In some embodiments, the orientation projection extends around the wheel and is connected to the body.

In some embodiments, the orientation projection is removeably connected to the body.

According to another aspect of the present invention there is provided a base for a guide device for guiding a tool-string comprising an elongate sensor assembly in a wellbore, the base comprising a first engagement portion for engaging an end of the tool-string and second engagement portion for engaging a nose assembly, wherein the base is shaped such that a nose assembly engaged, in use, with the second engagement portion projects away from the base at an angle which is offset to a longitudinal axis of the tool-string engaged, in use, with the first engagement portion.

In some embodiments, the base is formed as an integral element or component of one end of an orientation structure.

In some embodiments, the base is hollow or has an aperture therethrough.

According to another aspect of the present invention there is provided a guide device for guiding a tool-string in a wellbore, the tool-string provided, in use, with an orientation structure for orientating the sensor assembly in the wellbore, the guide device comprising a nose assembly having a base adapted to engage an end of the tool-string and a nose section arranged to project away from the base at a fixed angle which is offset to a longitudinal axis of the tool-string when the nose assembly is engaged with said tool-string.

In some embodiments, the fixed angle can be pre-set.

In some embodiments, the fixed angle can be pre-set to one of a plurality of predefined settings.

In some embodiments, the guide device comprises a locking pin engagable with the base and the nose assembly to lock the nose section at a selected angular setting.

In some embodiments, the nose assembly comprises a locking member provided with a plurality of locking pin apertures and the base comprises a plurality of locking pin apertures.

In some embodiments, the angle can be pre-set to between 1° to 60°.

In some embodiments, the angle can be pre-set to between 1° to 45°.

In some embodiments, the angle can be pre-set to between 1° to 20°.

In some embodiments, the angle can be pre-set to between 1° to 9°, more preferably between 3° to 9°.

In some embodiments, the nose section is formed from a resilient flexible material

In some embodiments, the material is a resilient elastomer material.

In some embodiments, the nose section is made from a material which is readily drillable by standard wellbore drilling equipment, for example nylon.

According to another aspect of the invention there is provided a guide device for guiding a tool-string in a wellbore, the guide device comprising a nose assembly having a base adapted to engage an end of the tool-string and a nose section having a tip which is offset from a longitudinal axis of the tool string when the nose assembly is engaged with said tool-string.

According to another aspect of the present invention there is provided a tool-string provided with the sensor transportation apparatus of the first, second or third aspect and/or the guide device of the fifth or sixth aspect.

According to another aspect of the present invention there is provided a tool-string provided with a sensor transport apparatus for transporting an elongate sensor assembly through a wellbore, and an orientation structure, wherein

-   -   the sensor transportation apparatus comprises at least one         engagement structure to connect the sensor transportation         apparatus to the sensor assembly, and one or more wheels         arranged to rotate about an axis of rotation substantially         perpendicular to a longitudinal axis of the sensor assembly when         the transportation apparatus is connected to the sensor         assembly, and wherein     -   the orientation structure defines a form that has a transverse         outline which has a rotational centre which is offset from a         centroidal axis of the elongate sensor assembly.

In some embodiments, the engagement between the sensor transportation apparatus and the sensor assembly substantially prevents relative rotation between the sensor transportation apparatus and the sensor assembly about the longitudinal axis of the sensor assembly.

In some embodiments, the orientation structure comprises a plurality of separate components.

In some embodiments, the sensor transportation assembly comprises at least one of the separate components of the orientation structure.

According to another aspect of the present invention there is provided a sensor transportation apparatus to convey an elongate sensor assembly through a wellbore, the sensor transportation apparatus comprising:

-   -   at least one engagement structure to connect the sensor         transportation apparatus to the sensor assembly, and     -   at least one friction reduction element for reducing friction         between the apparatus and the wellbore wall, and     -   an orientation structure defining a form having a rotational         centre, wherein the rotational centre is substantially parallel         to and offset from a centroidal axis of the elongate sensor         assembly.

In some embodiments, the friction reduction element comprises at least one skid.

In some embodiments, the friction reduction element comprises at least one wheel arranged to rotate about an axis of rotation which is substantially perpendicular to a longitudinal axis of the sensor assembly when the transportation apparatus is connected to the sensor assembly.

According to another aspect of the present invention there is provided a transportation apparatus comprising at least one engagement structure to connect the sensor transportation apparatus to the sensor assembly, and

one or more wheels arranged to rotate about an axis of rotation substantially perpendicular to a longitudinal axis of the sensor assembly when the transportation apparatus is connected to the sensor assembly, and

at least one protection structure which extends longitudinally around the wheel, to thereby substantially prevent a side of the wheel from contacting the wellbore wall, wherein the wheel extends above and below the protection structure.

In some embodiments, each wheel is mounted on an axle, more preferably a stub axle.

In some embodiments, each stub axle is engaged with a protection structure. Alternatively, the stub axle is integral with the protection structure.

In some embodiments, the wheel is mounted on an axle, and the protection structure has a height which is at least equal to a diameter of the axle, but less than a radius of the wheel.

In some embodiments, there is a clearance space between a surface of wheel which is at the radial extremity of the wheel, relative to the axis of rotation, and a body of the transportation apparatus, of at least 4 mm.

In some embodiments, there is a clearance space between a surface of wheel which is at the radial extremity of the wheel, relative to the axis of rotation, and an inner surface of the protection structure, of at least 4 mm, or preferably at least 10 mm, more preferably substantially 19 mm.

In some embodiments, the protection structure is an orientation projection.

According to another aspect of the present invention there is provided an apparatus for supporting, orienting and transporting an elongate sensor assembly in a wellbore, the apparatus comprising a body having at least one engagement structure releasably attachable to the sensor assembly and an orientation structure having one or more radial projections formed from the body corresponding to a substantially constant radius from a rotational centre,

wherein the rotational centre is offset from a centroidal axis of the elongate sensor assembly such that the eccentric mass of the sensor body causes the tool assembly to orientate toward the lower aspect of the wellbore.

According to a further aspect of the present invention there is provided a method of taking a wellbore measurement from an upper surface of a wellbore comprising positioning a sensor provided with an orientation structure as herein described inside the wellbore and operating the sensor to take the measurement.

According to a further aspect of the present invention there is provided an elongate sensor transportation apparatus substantially as herein described with reference to any one or more of the embodiments described herein and illustrated in the drawings.

According to a still further aspect of the present invention there is provided a guide device for guiding a tool-string substantially as herein described with reference to any one or more of the embodiments described herein and illustrated in the drawings.

The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

Further aspects of the invention, which should be considered in all its novel aspects, will become apparent from the following description given by way of example of possible embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

An example embodiment of the invention is now discussed with reference to the drawings in which:

FIG. 1 shows a isometric view of a sensor transportation apparatus as configured in accordance with a preferred embodiment of the invention.

FIG. 2 shows a side view of the transportation apparatus of FIG. 1

FIG. 3 shows a top view of the transportation apparatus of FIGS. 1 and 2.

FIG. 4 shows a cross-section along plane A-A of the transportation apparatus of FIGS. 1-3, and shows the integral lubrication delivery apparatus. The wellbore wall is shown in outline.

FIG. 5 shows a cross-section of an alternative embodiment along plane A-A. The wellbore wall is shown in outline.

FIG. 6a shows a front view of a transportation apparatus provided in accordance with an alternative embodiment to that shown in FIGS. 1-5, with the wellbore shown outline.

FIG. 6b shows a perspective view of the transportation apparatus of FIG. 6 a.

FIG. 7 shows a perspective view of a wireline tool-string engaged with both the transportation apparatus illustrated in respect to FIGS. 6a and 6b in addition to the apparatus shown with respect to FIGS. 1-4.

FIG. 8 shows an isometric view of a further embodiment of the transportation apparatus.

FIG. 9 shows a cross-section view of the embodiment shown in FIG. 8.

FIG. 10 shows a side view of a guide device provided in accordance with one embodiment of the invention.

FIG. 11 shows a front perspective view of the guide device of FIG. 10.

FIG. 12 shows a rear perspective view of the guide device of FIG. 10.

FIG. 13 shows an exploded side view of another embodiment of the guide device.

FIG. 14 shows an exploded perspective view of the guide device of FIG. 13.

FIG. 15 shows an isometric view of a base for a guide device.

FIG. 16 shows a perspective view of an embodiment of an adjustable guide device set to a 3° angle.

FIG. 17 shows the adjustable guide device of FIG. 16 set to an 8° angle.

FIG. 18 shows the adjustable guide device of FIG. 16 set to a 15° angle.

FIG. 19 shows exploded perspective view of another embodiment of an adjustable guide device.

FIG. 20 shows an isometric view of an orientation structure which is provided with low friction skids.

FIG. 21 shows an isometric view of another embodiment of an orientation structure which is provided with low friction skids.

FIG. 22 shows an isometric view of another embodiment of an orientation structure which is provided with low friction skids.

FIG. 23 shows an isometric view of another embodiment of an orientation structure which is provided with low friction skids.

FIG. 24 shows a transverse cross-section of another embodiment of an orientation structure which is provided with low friction skids.

FIG. 25 shows a transverse cross-section of another embodiment of an orientation structure which is provided with low friction skids.

FIG. 26 shows a transverse cross-section of another embodiment of an orientation structure which is provided with low friction skids.

FIG. 27 shows a transverse cross-section of another embodiment of an orientation structure which is provided with low friction skids.

FIG. 28 shows a perspective view of a guide device and orientation structure mounted to a wireline logging tool-string.

FIG. 29 shows a perspective view of the guide device of FIG. 28 in combination with an alternative orientation structure which is provided with low friction skids, mounted to a wireline logging tool-string.

FIG. 30 a perspective view of the guide device of FIG. 28 in combination with two orientation structures which are provided with low friction skids mounted to a wireline logging tool-string.

FIG. 31 a perspective view of the guide device of FIG. 28 in combination with transportation apparatus mounted to a wireline logging tool-string.

FIG. 32 shows a perspective view of a weight bar attached to a guide device according to FIG. 19 and three transport apparatus according to FIG. 41.

FIG. 33 shows a perspective view of a guide device according to FIG. 19 attached to a wireline tool-string, with a bowspring orientation structure.

FIG. 34 shows a perspective view of another embodiment of the guide device.

FIG. 35 shows a perspective view of a transportation apparatus with an integral lubrication delivery apparatus with one wheel and associated bearing shown in partially exploded form.

FIG. 36 shows a perspective view of the transportation apparatus in another embodiment.

FIG. 37 shows an isometric view of a transport apparatus configured as a tractor unit, with a jockey wheel in a raised position.

FIG. 38 shows a front view of the tractor unit of FIG. 37 in use in a wellbore, with a lower portion of the jockey wheel shown in hidden detail.

FIG. 39 shows a front view of the tractor unit of FIG. 37 in use in a wellbore with the jockey wheel in a lowered position, and with a lower portion of the jockey wheel shown in hidden detail.

FIG. 40 shows a perspective view of another embodiment of an orientation structure.

FIG. 41 shows a perspective view of a guide device and orientation structure mounted to a wireline logging tool-string which has a sampling tool on its upper surface.

FIG. 42 shows the same wireline logging tool-string as FIG. 42, but with wheeled transportation providing the orientation.

FIGS. 43A and 43B show a logging tool assembly 100 comprising a plurality of transportation apparatuses 1 and an orientation structure 24 mounted to an elongate sensor assembly 2. FIG. 43A is a perspective view from above and FIG. 43B is a transverse end view with the logging tool assembly 100 in a most stable position.

FIGS. 44A and 44B show another logging tool assembly 100 comprising a plurality of transportation apparatuses 1 and an orientation structure mounted to an elongate sensor assembly 2. FIG. 44A is a perspective view from above and FIG. 44B is a transverse end view with the logging tool assembly 100 in a most stable position.

FIGS. 45A and 45B show another logging tool assembly 100 comprising a plurality of transportation apparatuses 1 and an orientation structure 24 mounted to an elongate sensor assembly 2. FIG. 45A is a perspective view from above and FIG. 45B is a transverse end view with the logging tool assembly 100 in a most stable position.

FIGS. 46A and 46B show another logging tool assembly 100 comprising a plurality of transportation apparatuses 1 and an orientation structure 24 mounted to an elongate sensor assembly 2. FIG. 48A is a perspective view from above and FIG. 48B is a transverse end view with the logging tool assembly 100 in a most stable position.

FIGS. 47A to 47D show another logging tool assembly 100 comprising a plurality of transportation apparatuses 1 and an orientation structure 124 mounted to an elongate sensor assembly 2. FIG. 47A is a perspective view from above, FIG. 47B is a transverse end view with the logging tool assembly 100 in a most stable position, FIG. 47C is a bottom view, and FIG. 47D is a side view.

BEST MODES FOR CARRYING OUT THE INVENTION

FIGS. 1-4 show a number of views of the transportation apparatus 1 as provided. In this embodiment the transportation apparatus is arranged to connect over or on to the exterior surface of an elongate sensor assembly—shown in cross-section in FIG. 4 as a tool-string 2 used in a wireline logging applications. FIG. 4 also illustrates the position of the longitudinal axis 2 a of the tool-string 2. As used herein the phrase “elongate sensor assembly” includes both the sensors themselves, and any equipment attached to the sensors such as weights, spacers and flexible couplings.

FIG. 4 illustrates the perimeter walls of a wellbore 3 which the tool-string 2 is to be conveyed down by the transportation apparatus 1. For the sake of convenience the wellbore 3 is shown with a substantially horizontal orientation, with its low side 3 a shown at the bottom of the page.

The transportation apparatus 1 includes the main body 4, used to mount and locate the remaining elements or components of the apparatus.

FIGS. 1 through 3 show details of a pair of engagement structures formed in this embodiment by integral locking collars 5. These locking collars 5 are located at either end of the apparatus 1. Each collar 5 is arranged to partially enclose the exterior side wall surface of the tool-string 2, allowing the transportation apparatus to be slid on and over the tool-string at any desired position along the length of the tool-string. Each collar includes a series of threaded holes 5 a arranged to receive a screw which engages with a recess or blind hole in the exterior surface of the tool-string. These threaded holes 5 a and an associated set of screws are used to lock the apparatus 1 to the tool-string 2 with a specific orientation. By arranging the collars 5 to only partially enclose the tool-string 2, the tool-string can be carried in a lower position than would be possible if the collars 5 were to completely encircle the circumference of the tool-string 2. The body with threaded holes 5 a and screws provide an engagement structure to connect the transportation apparatus to the sensor assembly and prevent relative rotation between the sensor transportation apparatus as the elongate sensor assembly.

The main body of each of these collars also defines or forms a protection structure 14 which protects wheels deployed on either side of the body from impact and abrasion. These protection structures also serve to orientate the carriage and tool-string assembly in the wellbore. These protection structures can also prevent the space between the wheel and tool-string 2 catching on wellbore projections, such as the casing shoe, as the tool-string 2 is pulled up and out of the wellbore. As can be seen from at least FIG. 1 these protection structures may incorporate an angled surface projection 13 which can act to position the sensor assembly and transportation apparatus in the wellbore and guide the tool down the wellbore.

FIGS. 1 through 4 also show the provision of a pair of wheels 6 which form part of the transportation apparatus 1. These wheels 6 are deployed laterally adjacent to one another on opposite sides of a tool-string. In the embodiment shown each wheel rotates on a stub axle 7. The wheels 6 have an axis of rotation which is perpendicular to a longitudinal axis of the elongate sensor assembly. In the embodiment shown, the wheels have a common axis of rotation.

As can be seen from these figures each wheel 6 has a diameter substantially greater than one of the diameter, width or height of the tool-string 2. This allows each of the wheels 6 to make radial contact with the wall of the wellbore 3 (that is, the radial edge of the wheels makes contact with the wellbore wall). The large relative size of each wheel 6 lifts the tool-string 2 from the low side surface of the wellbore 3, allowing the transportation apparatus 1 to convey the tool-string 2 down the wellbore 3. These large wheels allow the transportation apparatus 1 to roll along rugose borehole walls, up and over obstructing ledges which would normally impede the progress of the wireline logging tool-string 2. The wheels are widely spaced in the wellbore with a broad wheel track which allows the wheels to bridge over obstructing wellbore cuttings which tend to sit on the low side of the hole 3 a. In preferred embodiments the wheels 6 extend below the main body 4 and below the sensor engaged with the apparatus, and thereby create a minimum clear space of at least 10 mm, more preferably at least ½ inch, between the tool string 2 (and the body) and the bottom of the wellbore.

FIG. 4 shows a cross-section view of the transportation apparatus of FIGS. 1-3 along the plane A-A shown in FIGS. 2 and 3. FIG. 5 shows similar view to FIG. 4 of a cross-section view of the transportation apparatus provided in a further embodiment. In the embodiment shown with respect to FIG. 4 a double set of ball bearing assemblies 10 are used, whereas in FIG. 5 the wheels rotate over a set of bushes 110.

FIGS. 4 and 5 show the positioning and arrangements of the axis of rotation of each wheel 6 as provided by stub axles 7. As can also be seen from these figures each of these stub axles 7 is located above the longitudinal axis 2 a of the tool-string 2. The longitudinal axis is essentially the axial or longitudinal centre of mass of the tool-string. As the tool-string 2 is much heavier than the transportation apparatus 1 the tool-string 2 will tend to rotate into the orientation shown in FIG. 4 where the transportation apparatus sits squarely on both wheels.

Identified on these figures is the rotational centre 15 of the transportation apparatus and the centroid 2 a or centre of mass of the tool-string. In the embodiment shown each section of the tool-string has a centre of mass 2 a approximately in the middle of the circular section of the tool-string. The rotational centre 15 of the transportation apparatus is located above the centroidal axis 2 a of the tool-string. The centroidal axis of the tool-string, as that phrase is used herein, is formed by the line joining the centre of mass of each cross-section along the length of the tool-string. The axis of rotation of the wheels 6 preferably passes through the rotational centre 15.

The body 4 also mounts an orientation structure comprising at least one orientation projection 8. As can be seen from FIG. 4 the orientation projection 8 assists in providing the tool-string 2 with a predictable orientation within the wellbore 3. If the tool-string 2 were to rotate to place the orientation projection 8 in contact with the low side of the wellbore 3 this would make the position of the combined transportation apparatus and connected tool-string 2 unstable. The orientation projection 8 therefore assists in positioning and orientating the tool-string in the arrangement shown in respect of FIG. 4. The radially extreme edges of the wheels 6 and the protection structure 14 also form part of the orientation structure and assist in orientating the tool-string in the orientation shown in respect to FIG. 4.

FIGS. 4 and 5 also show the form provided through a cross-section of the transportation apparatus made through all of its orientation projections 8, protection structures 14 and wheels 6. This form has a transverse outline (that is an outline or silhouette when viewed along the longitudinal axis of the sensor assembly) which has a rotational centre 15. The position of this rotational centre is the point which experiences the minimum vertical displacement when the form is rolled over a flat horizontal surface. In preferred embodiments the extremities of the orientation structure lie on a substantially circular imaginary curve centred on the rotational centre 15. The rotational centre of the transportation apparatus is offset from the centroid or centre of mass of the tool-string 2 a.

The offset between the rotational centre of the transportation device and centre of mass of the tool-string ensures the assembly is orientated in the most stable position with the tool-string centre of mass below the rotational centre of the transportation apparatus. In this stable position the tool-string descends down the wellbore carried on the wheels of the transportation apparatus. As shown in FIGS. 4 and 5, in the most stable position the tool-string 2 is closest to the low side of wellbore wall.

Referring in particular to FIG. 4, in this embodiment the rotation of each wheel 6 is lubricated by a pressurised lubrication system 9 as it rotates about a double set of ball bearing assemblies 10. FIG. 5 shows an alternative arrangement of the transportation apparatus where the lubrication system 9 acts on a set of bushes 110. This lubrication system 9 includes a lubricant reservoir 11 and pressurising plunger linked to the bearings 10 or bushes 110 by a pair of channels 12. In other embodiments the plunger may be replaced by a set of elastomer bellows, or by an elastic diaphragm, as is described further below. The plunger is maintained at a higher pressure than the surrounding wellbore fluids thereby force feeding lubricant to the wheel bearing or bush surfaces via the channels 12. Pressurisation of lubricant at this point in the apparatus prevents the entry of exterior contaminants from the wellbore 3.

FIGS. 6a and 6b show cross-section and isometric views of a transportation apparatus 201 provided in accordance with alternative embodiment to that shown in FIGS. 1-5. FIG. 7 shows an isometric view of a wireline tool-string 2 engaged with both the transportation apparatus illustrated in respect to FIGS. 6a and 6b in addition to the apparatus shown with respect to FIGS. 1-4.

In the embodiment of the apparatus shown in FIG. 6b the transportation apparatus 201 is arranged to engage with the bottom end or nose of a tool-string, thereby forming the leading component deployed down a wellbore. In this embodiment of the transportation apparatus 201 includes a single wheel 206 deployed as the leading component of the apparatus. This single wheel can act as a hole finding assembly which can encounter and then roll over the top of obstacles immediately in the path of the tool-string. As can also be seen from FIGS. 6a and 6b the wheel 206 has a scalloped or concave profile, allowing it to bridge cuttings and obstacles encountered in the middle of the low side of the wellbore. The wheel is scalloped to ensure that only the edges of the wheel contact the wellbore wall resulting in a wide wheel track width, lower rolling friction and greater stability in the operating position. The single wheel providing two spaced apart edges in contact with the wellbore wall may be considered as a pair of integrally formed wheels.

The axis of rotation of the wheel 206 is above the centreline or longitudinal mid-line axis 202 a of the tool-string which defines the longitudinal or axial centre of mass of the tool-string.

Furthermore, the apparatus 201 has an orientation structure which in this embodiment comprises multiple orientation projections 208 arranged to assist in maintaining this desired orientation of the tool-string. The orientation projections 208 a also function as protection structures and protect the wheels. As can be seen in FIGS. 6a and 6b , one or more of the orientation projections 208 a may also provide a mounting point for mounting the wheel 206 or wheel axle.

FIG. 6a also shows the form provided through a cross-section view of the transportation apparatus 201 made through all of its orientation projections 208 and the end view of wheel 206. This form has a transverse outline with a rotational centre 207. The rotational centre is substantially parallel to and offset from a central axis of the elongate sensor assembly. The rotational centre of the transportation apparatus is offset from the centroid or centre of mass of the sensor assembly/tool-string 202 a.

As with the embodiments described above, the offset between the rotational centre of the transportation device and centre of mass of the tool-string ensures the assembly is orientated in the most stable position with the tool-string centre of mass below the rotational centre of the transportation device. In this stable position the tool-string descends down the wellbore carried on the wheels of the transportation device.

FIG. 7 shows how these two different implementations of the transportation apparatus can be deployed in conjunction with a single tool-string 2 to form a system for transporting the tool-string. The single wheeled apparatus 201 is used to lift the bottom end or nose of the tool-string while the paired wheels of the transportation apparatus 1 is used to carry the upper section of the tool-string 2. In another embodiment the transportation apparatus may be provided with a partial orientation structure, or no orientation structure at all. In these embodiments a separate component may carry some or all of the orientation structure. For example, a tool-string may be provided with a transportation apparatus and one or more of the orientation structures shown in FIG. 20, 21 or 33. The relative positioning of the separate components of the orientation structure along the sensor assembly is not critical, provided the overall form has a transverse outline with a rotational centre.

FIGS. 8 and 9 show an alternative embodiment of the transportation apparatus 1 a. This embodiment is configured for in-line connection to a sensor assembly, rather than mounting over the sensor or other sensor assembly component. As can be seen, the transportation apparatus 1 a is provided with an orientation structure which includes a protection structure which includes removable orientation projections 8 a which extend from in front of the wheels, around an exterior surface 6 a of the wheels 6. These orientation projections 8 a are shaped to assist in preventing material from clogging the space between the inside surface of the wheel 6 b and the corresponding exterior surface of the main body 4 a.

The width of the wheels 6 is preferably allows a clearance space between the inner surface of the wheel and the body, and between the outer surface of the wheel and the protection structure. In a preferred embodiment there is at least 4 mm clearance between the operating surface of the wheels and the surrounding body and structure, as is described further below.

As is best seen in FIG. 9, in this embodiment the orientation projections 8 a also operate to support the outer ends of the stub axles 7 on which the wheels 6 are mounted. Those skilled in the art will appreciate that in an alternative embodiment (not shown) the stub axles 7 may be permanently connected to or integral with the removable orientation projections 8 a, and may be engaged with and supported by the body 4 a at their inner ends.

As shown in the cross-section view of FIG. 9, the wheel 6 diameter is greater on the inner face 6 b than the outer face 6 a to fit to the circular wellbore profile. This variation in wheel diameter causes some skidding at the contact surface between the wheel and the wellbore wall as the wheel rotates. Preferably the wheel should be narrow in order to minimise skidding contact and provide the least friction between the wheel and the wellbore wall as the wheel rotates down the wellbore. As can be seen from these figures, the width of the wheels 6 is less than about 20 mm, preferably less than 18 mm. In one embodiment shown in FIG. 9 the wheel width is 10 mm. In another preferred embodiment shown in FIG. 42 the wheel width is 15 mm.

FIGS. 10 to 12 show a number of views of a guide device 21. The guide device 21 includes a nose assembly 22 formed from a nose section 23 and a base 27, as shown in FIGS. 10 and 11. Directly attached to the nose assembly 22 is an orientation structure 13, provided in the embodiment shown by an orientated stand-off 24.

The orientated stand-off 24 provides a sleeve like structure with a hollow interior cavity 29 arranged to receive the leading end of the wireline logging tool-string. The orientated stand-off 24 includes a pair of friction reducing elements, in this case travel skids 26, which are oriented to slide along the downside wall of the wellbore through the action of a set of three orientation projections 8 provided by the orientated stand-off 24. In the embodiment shown the travel skids 26 are formed from a durable ceramic material which has low friction characteristics and resists abrasion, and the effects of high temperatures and high alkaline conditions found in a wellbore, for example alumina ceramic or polymetallic oxide thermosetting ceramic. In other embodiments suitable plastic or elastomer materials can also be used for this component. When provided with such friction reducing elements the orientated standoff 24 can function as a transportation apparatus, although wheels may be necessary for high deviation angles.

The travel skids, when provided, may be designed for use in a specific wellbore diameter, and may be shaped to conform to the curvature of the wellbore wall. The leading and trailing edges of the travel skids are contoured to form a gentle entry to allow the skids to “ski” over mudcake and cuttings debris.

The travel skids are positioned on the orientated standoff so that they do not travel over the lowermost section of the wellbore where cuttings are likely to accumulate. Rather, the skids straddle the cuttings and are positioned laterally in on the borehole wall, preferably between 30° and 45° from a vertical plane through the longitudinal axis of the sensor assembly.

The orientation structure 24 comprising the projections 8 has an engagement structure to connect the orientation structure to the tool-string to prevent relative rotation between the structure 24 and the tool-string. As described above, the engagement structure may comprise threaded holes and associated screws to engage the tool-string to lock the structure 24 to the tool string, as described with reference to FIG. 40. As is described above with reference to FIGS. 1 to 4, the orientation projections 8 act to destabilise the position of the tool-string if placed in contact with the low side wall of a deviated wellbore. The substantial weight of the tool-string will ensure that if one of these projections is in contact with the down side wall, the tool-string will rotate back about it's longitudinal axis to an orientation placing the travel skids in contact with the downside wall.

As can be seen from FIGS. 10 to 12, the nose section 23 has a fixed offset angle relative to the longitudinal axis of any tool-string engaged with the interior cavity 29 of the orientated stand-off 24. This arrangement provides the nose section 23 with a permanent upward inclination as the combined guide device and tool-string is deployed down a deviated wellbore. The upward inclination of the nose section ensures that the nose section tip 36 is elevated above the low side of the wellbore by a height 37, and is offset from and above the longitudinal axis of the tool-string. Hence obstacles on the low side wall of the wellbore are avoided by the guide device with the tool-string following immediately after the nose assembly.

FIGS. 13 and 14 show an exploded view of a further preferred embodiment of the guide device. The guide device includes a nose section 23, a base 27 and an orientation structure 24. All three components may be partially or fully integrated (not shown) or provided as discrete components as in the embodiment shown. In the embodiment shown the base 27 has a fixed angle relative to the tool-string longitudinal axis and is attached directly to the leading end of the wireline logging tool-string. The nose section 23 is attached to the terminal end of the base 27. The orientation structure slides over and is attached to the logging tool-string such that the orientation projections are aligned to orient the nose section 23 upwards as the tool-string descends down the wellbore.

The nose section 23 can be implemented in different lengths, thereby altering the height 37 from the bottom of the wellbore to the nose section tip 36. The offset of the nose section tip 36 is pre-set depending on the wellbore size and conditions.

An enlarged view of one embodiment of the base 27 is shown in FIG. 15. The base 27 may be used with some nose sections of the prior art in order to provide improved performance, although those skilled in the art will appreciate that the tool-string will require some type of orientation structure, for example an orientated stand-off, bow spring eccentraliser and/or transportation apparatus as described herein, in order to orientate the nose away from the base of the wellbore.

The base 27 has a first engagement portion 25 a for engaging an end of a tool-string, and a second engagement portion 25 b for engaging a nose assembly. The engagement portions have centrelines which are angularly offset, such that a nose assembly engaged, in use, with the second engagement portion 25 b has a centreline which extends at an angle to the centreline of a tool-string engaged with the first engagement portion 25 a, as can be seen in FIG. 13. The offset angle maybe any suitable angle, depending on the length of the nose assembly and the diameter of the wellbore, as is described further below.

In this embodiment the first engagement portion 25 a is provided as a collar which fits over a standard boss provided at the end of a tool-string, and the second engagement portion 26 b is provided as a hollow boss having standard outer dimensions for engaging a collar provided at the end of a prior art nose assembly. The base 27 is itself hollow, or at least has an aperture therethrough, to allow wiring to be passed through the base 27 if necessary.

FIGS. 16 to 18 show different configurations of angle nose assembly capable of being used in the embodiments shown in FIGS. 28-33. The nose assembly can rotate or pivot about an axle 38 which is engaged to the base 27, so that the angle of the nose assembly can be pre-set to a selected angle before the tool-string is lowered into the wellbore. The base 27 has a locking arm (not shown) extending inside the nose section 23. The nose section is set at a fixed pre-set angle from the longitudinal tool axis by a locking pin extending through one of three locking points 30 to connect with the locking arm. The nose section pivoting connection 38, combined with the locking point 30, secures the nose section to the base 27 at a fixed angle from the tool-string longitudinal axis. The selection of locking point 30 will determine the offset angle and hence the heights 37 of the nose section tip 36 above the low side of the wellbore.

As can be seen from FIGS. 16-18, each fixed angle setting of the nose assembly 22 provides the nose section 23 with a different offset angle. The offset angle implemented by each nose section 23 increases from 3° in FIG. 16, 8° in FIG. 17 and 15° and FIG. 18. Those skilled in the art will appreciate that the pre-set angle may be adjusted depending on the diameter of the wellbore, the required standoff of the tool-string in the wellbore, and the length of the nose assembly, to locate the end of the nose assembly in a suitable position in the wellbore. Longer nose assemblies will require shallower angles, and shorter nose assemblies will require larger angles, for a given wellbore diameter and standoff distance. The angle is selected such that the tip of the nose section is above the longitudinal axis of the tool-string.

FIG. 19 shows an alternative embodiment of an adjustable nose assembly. In this embodiment the nose section 23 is provided with a locking member 31. A pin or axle 38 extends through apertures in the base 27 and the locking member 31. The base 27 has a vertically orientated longitudinal slot 33 to accommodate the locking member 31.

The end of the locking member 31 is provided with a plurality of locking pin apertures 34 a which are parallel to the aperture for the axle 38. Locking pin apertures 34 b are also provided in the base 27. The locking pin apertures 34 a, 34 b are arranged such that one of the apertures 34 a in the locking member 31 is aligned with one of the apertures 34 b in the base 27 when the nose section 23 is set to one of a predetermined number of angles. The nose section 23 is held at the required angle by inserting a locking pin 34 through apertures 34 a, 34 b. In a preferred embodiment the apertures 34 a, 34 b are arranged to allow the nose section to be set to angles of 3 degrees, 6 degrees or 9 degrees to the centreline of the tool-string, although other embodiments may provide angles up to 60°, 45° or 20°. Angles as low as 1° may be used in some embodiments, although often this will require the use of an inconveniently long nose assembly.

FIGS. 20-23 show perspective views of two different types of orientation structure provided in accordance with a yet further embodiment. These figures again illustrate the different forms of orientated stand-off 24 which are to be provided as orientation structures for orienting a tool string or guide device.

These different orientated stand-offs cater for different sizes or diameters of wellbore size. These figures also illustrate different arrangements of orientation projections 8.

The stand-offs shown in FIG. 20 and FIG. 22 employ a set of four orientation projections 8, while the stand-offs 24 shown in FIGS. 21 and 23 employ three orientation projections only. The orientation projections 8 have tapered extremities 35 (at upper and lower ends with the tool string vertically run down a well bore) to assist in guiding the tool-string around or past obstacles encountered in a wellbore.

The oriented standoffs have a hole 29 passing through the body of the device. This hole is offset from the nominal centre of the standoff. The oriented standoff is designed to slip over a cylindrical wireline logging tool which is then fixed within the hole 29, and below the rotational centre of the stand-offs. The tool-string will therefore be conveyed with a predictable orientation, which in turn will impart an upward orientation or angle to the nose section of the nose assembly.

FIGS. 24-27 show a series of transverse or cross-section views of a number of different implementations of orientation structures. These orientation structures are capable of being used in the embodiments shown with respect to FIGS. 10-19 and 28-30. Identified on these figures is the rotational centre 15 of the orientation structure and the centroid 2 a or centre of mass of the tool-string. In the embodiment shown each section of the tool-string has a centre of mass 2 a approximately in the middle of the circular section of the tool-string.

These figures also show the form provided through a transverse cross-section of each orientated stand-off made through all of its orientation projections 8 (which in these embodiments also corresponds to the transverse outline). The form provided by this cross section therefore has rotational centre 15. The rotational centre of the oriented standoff is offset from the centroid or centre of mass of the tool-string 2 a.

In a deviated wellbore the tool-string will naturally rotate about its longitudinal axis to seek the most stable position. The most stable position is where the tool-string and oriented standoff assembly has the lowest centre of gravity. The lowest centre of gravity is where the tool centroid is below the centre of rotation. In this stable position, the guide device nose section is orientated upwards, the low-friction travel skids of the orientated standoff are in contact with the low side of the wellbore and the logging tool sensors can be optimally orientated to measure the preferred side of the wellbore.

These views show various arrangements of orientated stand-offs with different numbers of orientation projections 8. As can be seen from these figures an orientated stand-off may be implemented with a number of different arrangements of orientation projection. These projections can also be formed with a variety of lengths to accommodate a range of different wellbore diameters.

As can also be seen from the embodiment displayed in these figures, in these embodiments the extremities of each of the orientation projections 8 define sections of the perimeter of a substantially circular curve centred on a point above the centre of gravity of any tool-string engaged with the orientation structure. In the embodiments shown, each of the projections 8 is arrayed at an equal angle to that of its neighbouring projections. However, the travel skids 26 are preferably arranged to have a greater spacing between them than the spacing between the other orientation projections, in order to maximise the stability of the apparatus when it is in its preferred orientation.

FIGS. 28-31 demonstrate the use of the guide device. The figures show the guide device displayed in FIGS. 16-18 and an associated wireline logging tool-string. These figures show a variety of embodiments where an orientation structure 24 or structures are connected to a tool-string 2 at positions remote from a nose assembly 22.

FIG. 28 illustrates the use of a single orientation structure, shown in this embodiment by an orientated stand-off 24 which is connected some distance away from a nose assembly 22. FIG. 29 illustrates a similar alternative arrangement of orientated stand-off 24 which is arranged to be deployed in a larger diameter wellbore than the stand-off shown with respect to FIG. 28, and hence has the nose 23 set at a larger angle and uses a larger diameter orientation structure.

FIG. 30 shows in a further embodiment which employs a pair of orientated stand-offs 24 located at two different positions along the length of a tool-string 2.

In the embodiment shown in FIG. 31 a pair of transportation apparatus 1 are used to orientate the guide device 21. The transportation apparatus 1 again act to provide the tool-string 2 with a predictable orientation and to impart an upward inclination to the nose section 23 of the nose assembly 22, as is described above with reference to FIGS. 1-9. Two or more transportation apparatuses may be provided to the tool-string depending on its length, to support the tool string along its length to be held above the low-side of the wellbore. As described earlier, each transportation apparatus is connected to the tool string via an engagement structure to prevent rotation between the transportation apparatus and the elongate sensor assembly. As shown in FIG. 31, the transportation apparatuses 1 are fixed to the tool-string in the same orientation. Thus, the axles and axes of rotation of the wheels of the transportation apparatuses spaced apart along the elongate sensor are parallel in a transverse view of the tool-string assembly. One skilled in the art will understand that FIG. 4 provides a transverse cross sectional view through the axis of rotation of the wheels of the transportation apparatus nearest the guide 22 back towards the apparatus furthest from the guide. In FIG. 31 the axles are parallel and aligned to be colinear, i.e. the rotational axes are in plane.

FIG. 32 shows a variation of the system shown in FIG. 31. In this embodiment the transport apparatus 1 are attached to a weight bar 39. The weight bar 39 is attached to a tool-string 2, preferably by a flexible coupling. This allows the transport apparatus 1 and guide device 21 to be used with any type of tool-string, including those with sensors that must be touching the borehole wall, those with irregular profiles, and exceptionally large diameter tools relative to the wellbore diameter. Tools that require lateral movement in the wellbore during operation may also be used, for example sampling tools which move across wellbore when set, and imager tools that are run in hole collapsed and open out to be centralised when deployed.

FIG. 33 shows another embodiment in which the orientation structure includes the use of a bowspring eccentraliser as an orientation projection 8. Bowspring eccentralisers are well known to those skilled in the art.

Referring next to FIG. 34, an embodiment of the guide device 21 is shown which has a base 27 b which has provision for mounting a temperature sensor 40 and/or other sensor means which require direct contact with the fluid in the wellbore. The base 27 b has a guard structure 41 comprising two parallel ribs 42 arranged on either side of the sensor 40, the ribs 42 extending at least as far from the body of the base 27 b as the sensor 40. This allows the temperature sensor probe to extend into the central area of the wellbore without risk of damage resulting from contact with the wellbore wall. In this position the temperature sensor assembly is well flushed by the movement of the tool through the wellbore fluids, and is not liable to be so covered with mudcake as to unduly affect response times. To ensure a fast response to temperature changes, preferentially the temperature sensor probe housing is made from a high thermal conductivity, low corrosion material such as low Beryllium Copper alloy, silver or gold.

The temperature sensor probe is preferably thermally insulated from the base and body of the guide device 21.

By positioning the probe at the end of the nose of the tool-string the probe measures wellbore temperature before that temperature is influenced by the temperate of the tool-string itself, and mixing of well fluids caused by the tool-string movement.

A pressure sensor may also be provided (additionally or alternatively to the temperature sensor). The provision of a pressure sensor which does not become clogged with mudcake or other debris allows the change of depth of the tool to be monitored. In this way the operator can ensure that the tool-string is proceeding into the wellbore at a rate which is consistent with the rate at which the cable feed is operating. Feeding cable at too high a rate can result in the cable becoming tangled and the tool-string becoming difficult to remove from the wellbore.

The sensor 40 is positioned so as to be behind the upwardly angled nose section 23. Because the orientation structures keep the nose section 23 angled upward, and the nose section 23 is held at a fixed angle when in use, the sensor 40 does not come into contact with the sides of the wellbore, and is shielded by the nose section 23 from any steps or shelves in the wellbore walls. In the embodiment shown the guide device 21 is provided with the pre-set angle adjustment system described above with reference to FIG. 19, and shows the cover plate 43 which is used to retain the locking pin 34.

The transportation apparatus 1 may include a lubrication delivery apparatus to provide lubrication to the wheels, as described in PCT/NZ2013/000210, which is incorporated herein by reference. For example, the transportation apparatus shown in FIGS. 35 and 36 is provided with lubrication system 300. The apparatus 1 is also provided with a protection structure in the form of removable orientation projections 8 a which extend around an exterior surface 6 a of the wheels 6, as described above with reference to FIGS. 8 and 9. These orientation projections 8 a extend substantially longitudinally from in front of each wheel to behind the wheel, and are shaped to assist in preventing material from clogging the space between the inside surface of the wheel 6 b and the exterior of the main body, and support the outer ends of the stub axles 7 on which the wheels 6 are mounted, as is described above. As can be seen in these figures, the wheels 6 extend above and below the longitudinally extending orientation projection 8 a. The longitudinally extending orientation projection 8 a is preferably relatively slender, for example having a height which is greater than the diameter of the axle on which the wheel is mounted, but less than the radius of the wheel. As is best seen in FIG. 36, a clearance space is provided between the radially extreme edge or surface 67 of the wheel (relative to the axis of rotation) and the longitudinal orientation projection 8 a, although the profile of the wheel may mean that the clearance is reduced towards the centre of the wheel.

This clearance, along with the slender aspect of the protection structure, assists in preventing the area inside the protection structure from becoming clogged with debris from the wellbore surface. In a preferred embodiment there is a clearance of at least 4 mm between radially extreme surface 67 of the wheel (that is, the surface of the wheel which is normally in contact with the wellbore wall) and the exterior of the main body, and at least 4 mm clearance between the radially extreme edge of the wheel and the interior of the protection structure. In the embodiment show the interior of the protection structure has a clearance of at least 15 mm, more preferably at least 19 mm.

The longitudinally orientated orientation projection preferably has a central axis which is substantially coincident with the rotational axis of the wheel.

FIGS. 37 to 39 show another embodiment of the transportation apparatus, in this embodiment configured as a tractor unit.

The tractor unit 400 comprises a transportation apparatus with a plurality of main wheels 6, in this case four main wheels 6, and at least one jockey wheel 6 c. The tractor unit preferably comprises an orientation structure having at least two orientation projections. Those skilled in the art will appreciate that the jockey wheel 6 c also functions as an orientation projection.

The jockey wheel 6 c is preferably mounted to an adjustable mounting means (not shown) for raising and lowering the jockey wheel relative to the main body 4 a. One or more of the main wheels 6, and preferably each of the main wheels 6, are connectable to a drive means, typically one or more electric motors. In a preferred embodiment the main wheels 6 are provided with clutch means (not shown) which can disengage the main wheels 6 from the drive means to allow the main wheels 6 to freewheel when the borehole is sufficiently steep.

In use, one or more tractor units 400 are connected in line with the tool-string. The tool-string and tractor 400 can free-wheel down the wellbore until the tool-string can no longer descend under gravity alone. At this point the jockey wheel 6 c is raised and extends upward to make contact with the top of the wellbore wall 3 (best seen in FIG. 38) thereby increasing contact pressure on the driven wheels 6. The clutch is engaged and the main wheels 6 are driven by the drive means. In this way the tool-string can be transported along wellbores at very high deviation angles, up to and including substantially horizontal wellbores. The tractor unit is preferably provided with a guide device 21 as described above. One or more transportation means 1 may also be used as required to assist in transporting the tool-string.

FIG. 40 shows another embodiment of an orientation structure which is provided as an orientated standoff 24, similar to those shown in FIGS. 20 and 21. In the embodiment shown in FIG. 40, the engagement between the standoff 24 and the tool-string is similar to that used with the transportation apparatus described above with respect to FIGS. 1-3. The engagement structure 5 is in the form of a locking collar. The collar 5 is arranged to partially enclose the exterior side wall surface of the tool-string 2, allowing the standoff to be slid on and over the tool-string at any desired position along the length of the tool-string. Each collar includes a series of threaded holes 5 a arranged to receive a screw which engages with a recess or blind hole in the exterior surface of the tool-string. These threaded holes 5 a and an associated set of screws are used to lock the apparatus 1 to the tool-string 2 with a specific orientation. By arranging the collars 5 to only partially enclose the tool-string 2, the tool-string can be carried in a lower position than would be possible if the collars 5 were to completely encircle the circumference of the tool-string 2, and allows an increased clear space 65 (preferably at least 10 mm, more preferably at least % inch) between the lower orientation projections 8, which in this embodiment comprise low friction skids, This clear space allows the cutting debris which has collected on the bottom surface of the bore to pass under the tool-string 2. As with the other orientation structures described above, the structure shown in FIG. 40 has a centre of rotation which is offset from the centroid of the tool-string 2.

FIGS. 42 and 43 show a variant of the system shown in FIG. 32. In this embodiment the tool-string is provided with a prior art sampling tool 66 for taking samples and pressure measurements. Because the tool-string 2 is connected to at least one orientation structure, whether an orientated standoff 24 or a transportation apparatus 1, the sampling tool can be orientated to take its sample from the high side of the wellbore. This has the advantage that the high side of the wellbore tends to be less damaged by the grinding action of the drillpipe as it rotates and reciprocates during the drilling operation. This damage can affect the porosity and permeability of the wellbore wall in particular, and can lead to unrepresentative measurements, or at least delays in obtaining representative measurements. By using the apparatus shown, this sampling process is improved.

Further example embodiments are now described.

As described earlier, a logging tool-string assembly may be provided with one or more transportation apparatuses and one or more orientation structures. FIG. 43A illustrates an example logging tool-string assembly 100 comprising an elongate sensor assembly 2 with four transportation apparatuses 1 spaced apart along its length and a single orientation structure 24. Each transportation apparatus 1 and the orientation structure 24 are fixed to the elongate sensor assembly 2 to prevent relative rotation, and with the axles of the transportation apparatuses parallel. Additional orientation structures could be also be fixed to the elongate sensor assembly. FIG. 43B illustrates a transverse end view from the nose end (downward end) of the logging tool assembly. With the orientation structure(s) 24 and transportation apparatus(es) 1 fixed to the elongate sensor assembly 2, the logging tool string assembly 100 presents a transverse outline with a rotational centre 15 offset from the centre or centre of mass 2 a of the elongate sensor assembly 2, to ensure the logging tool-string assembly 100 is oriented in the most stable position with the centre of mass 2 a below the rotational centre 15, as shown in FIG. 43B. In the illustrated embodiment the orientation structure 24 has a plurality of orientation projections 8 a. The outer or lateral extremities 108 of the projections 8 lie on a substantially circular curve. In the transverse outline, the bottom lateral extremities 108 of the transverse outline provided by the wheels 6 also lie on the substantially circular curve.

A curve drawn through the lateral extremities 108 of the transverse outline has a radius of curvature substantially less than the radius of curvature of the wellbore wall 3. The curve has a rotational centre or centre of curvature 15. The rotational centre is offset from the centre of mass 2 a of the elongate sensor assembly. When in the stable position, the transverse outline of the logging tool assembly provided by the orientation structure 24 and the wheels of the transportation device 1 presents only two spaced apart points of contact with the wellbore wall, a contact point between the bottom of each wheel 6 and the wellbore wall 3, as shown in FIG. 43B. There are no other points of contact between the transverse outline of the logging tool assembly and the wellbore wall. With the logging tool assembly in a position other than the most stable position there is also one or more points of contact between the transverse outline of the logging tool assembly 100 and the wellbore wall 3. The contact points are provided by lateral extremities of the transverse outline of the logging tool assembly 100. Here the term ‘point’ is not intended to be limited to only a precise point contact but to mean more generally a location or position of the wall of the wellbore.

The shortest distance between the centre of gravity 2 a of the elongate sensor assembly 2 and the wellbore wall 3 is when the pair of wheels 6 of the transportation apparatus 1 is in contact with the wellbore wall 3. In the most stable position with the logging tool assembly 100 carried on the wheels 6, the centre of mass of the elongate sensor assembly 2 is closest to the low side of wellbore wall 3. The centre of mass 2 a of the elongate sensor assembly 2 is further from the low side of the wellbore wall 3 when the logging tool assembly 100 is in any orientation within the wellbore other than the most stable position. With the logging tool oriented on its side, or up-side-down, or in any other orientation within the wellbore other than the most stable position, the centre of mass of the elongate sensor assembly will be a greater distance from the low side of the wellbore than when in the most stable position. This arrangement results in the mass of the elongate sensor assembly gravitating to the low side of the wellbore with the logging tool assembly 100 on its wheels, and maintaining this most stable orientation with the elongate sensor assembly located nearest to the low side of the wellbore, to traverse down the wellbore on its wheels.

As shown in FIG. 43B, a curve 101 having a radius of curvature equal to a radius of curvature of the wellbore wall 3 drawn between the bottom of the wheels 6 in the transverse outline of the logging tool assembly 100 presents a first distance 102 on a radial line between the curve 101 and the centre of mass 2 a of the elongate sensor assembly 2, and a curve 101 having a radius of curvature equal to a radius of curvature of the wellbore 3 drawn between any other two adjacent lateral extremities 108 of the transverse outline presents a second distance 103 between the curve 101 and the centre of mass 2 a of the elongate sensor assembly. The first distance 102 is shorter than the second distance 103. This arrangement of the lateral extremities 108 of the transverse outline of the logging tool assembly achieves a single most stable orientation with the assembly running on its wheels with the elongate tool string closest to the low side of the well bore.

For each orientation projection 8, a distance 105 between the lateral extremity 108 of the orientation projection 8 and the centre off mass 2 a of the elongate sensor assembly 2 is greater than a distance 102 on a radial line between the centre of mass 2 a of the elongate sensor assembly 2 and a curve 101 having a radius of curvature equal to a radius of curvature of the wellbore 3 drawn between the bottom of the wheels 6 in the transverse outline of the logging tool assembly.

More or less orientation projections 8 may be provided. For example, in the transverse view, the orientation structure 24 may present a single orientation projection 8 that extends radially outwards between the wheels in the transverse view. In an embodiment comprising a single orientation projection, the projection is preferably on a centreline of the tool-string assembly, and preferably perpendicular to the rotational axis of the wheels 6. The projection 8 a preferably extends radially with respect to the centre of rotation 15 and preferably radially with respect to the centre 2 a of the elongate sensor assembly 2.

FIGS. 44A and 44B and FIGS. 45A and 45B present further example logging tool-string assemblies 100 with an orientation structure 24 comprising a single orientation projection 8 extending radially between the wheels in the transverse view of the tool-string assembly. In the embodiment of FIGS. 44A and 44B, the projection 8 is positioned to extend radially between the wheels in a transverse outline of the logging tool assembly. In the embodiment of FIGS. 45A and 45B, the projection 8 is positioned to extend radially between the wheels and also radially outside of the lateral facing side 106 of each wheel 6 in a transverse outline of the logging tool assembly 100. In FIGS. 45A and 45B the orientation projection extends circumferentially around the apparatus from a vertical centre of the apparatus 100 to below the axis of rotation of the wheels.

The orientation structure fixed to the elongate sensor assembly provides a logging tool assembly 100 with an assymetric transverse outline with respect to the centre of mass 2 a of the elongate sensor assembly. The assymetric transverse outline is closest to the centre of mass 2 a of the elongate sensor assembly 2 between the bottom of the wheels of the sensor transportation apparatus.

As shown in FIG. 44B, a distance 105 between the lateral extremity 108 of the orientation projection 8 and the centre off mass 2 a of the elongate sensor assembly 2 is greater than a distance 104 between the centre of mass of the elongate sensor assembly and an outer side 106 of each wheel 6 of the transportation apparatus 1.

In the embodiments of FIGS. 43A to 45B the elongate sensor assembly 2 comprises a sampling tool 66 for taking samples and/or measurements from the wellbore and/or wellbore wall. An example of such measurements is resistivity, density or speed of sound of the rock formation penetrated by the wellbore. Samples may be the fluid contained in the pore spaces of the rock formation or cored plugs of the rock formation. In the illustrated embodiment, in the most stable position with the logging tool-string assembly 100 positioned on the wheels 6 of the transportation apparatuses 1, the sampling tool 66 is oriented to take a sample from a high side of the wellbore.

FIGS. 47A to 47D illustrate a further embodiment of a logging tool assembly 100 comprising a plurality of transportation and an orientation structure 124 comprising a single orientation projection 8 extending radially between the wheels in the transverse view of the tool-string assembly. The orientation structure 124 comprises a bow spring eccentraliser, and the bow spring presents a lateral orientation projection 8.

In the embodiment of FIGS. 47A to 47D the elongate sensor assembly 2 comprises a sampling tool 66 for taking samples and/or measurements from the wellbore and/or wellbore wall. In the most stable position with the logging tool-string assembly 100 positioned on the wheels 6 of the transportation apparatuses 1, the sampling tool 66 is oriented to take a sample from a low side of the wellbore. Orientation of the logging tool assembly allows for the sampling tool to be oriented to take a sample from any desired orientation of the wellbore, for example a horizontal side of the well bore (i.e. the high side or the low side), or any other desired side such as from a vertical side of the well bore 3.

In the embodiments shown in FIGS. 43A to 45B the rotational axis of the wheels extends through the centre 2 a of the elongate sensor assembly. However, the axis of the wheels may be below, on, or above the centre of the elongate sensor assembly. For larger wheels, the axis of rotation is preferably above the centre of gravity 2 a of the sensor assembly. Where the wheels are of a size such that the top and bottom of the wheels present lateral extremities together with the lateral extremities of the one or more orientation projections 8 in the transverse outline of the logging tool assembly, the rotational axis of the wheels extends through the rotational centre 15 of the transverse outline of the logging tool-string assembly 100, offset from and above the centre of mass 2 a of the elongate sensor assembly 2, as shown in FIG. 43A. For smaller wheels, the top of each wheel may not present a lateral extremity of the transverse outline of the logging tool assembly 100, in which case the lateral extremities of the transverse outline of the logging tool assembly 100 are provided by the bottom of the wheels 6 and the lateral extremities of the one or more orientation projections 8, and the axis of rotation of the wheels may be offset from the rotational centre 15 of the transverse outline of the logging tool assembly 100 and may be on or below the centre of mass 2 a of the elongate sensor assembly when the logging tool assembly 100 is in the most stable orientation. FIGS. 47A to 47D present an embodiment where the axis of rotation of the wheels 6 is below the centre of mass 2 a of the elongate sensor assembly.

Preferably the diameter of the wheels 6 is larger than the diameter of the elongate sensor assembly. Preferably the diameter of the wheels is as large as possible to reduce rolling resistance over a rugose wellbore wall. In alternative embodiments, one or more transportation apparatuses 1 may have skids rather than wheels, on which the logging tool assembly 100 is carried down the wellbore.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”.

Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents, then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the spirit or scope of the appended claims. 

The invention claimed is:
 1. A logging tool assembly comprising: an elongate sensor assembly, a plurality of sensor transportation apparatuses for transporting the elongate sensor assembly through a wellbore, the sensor transportation apparatuses spaced apart along the elongate sensor assembly, wherein each sensor transportation apparatus comprises: an engagement structure to connect the sensor transportation apparatus to the elongate sensor assembly and prevent relative rotation between the sensor transportation apparatus and the elongate sensor assembly, and one or more pairs of wheels arranged to rotate on an axis of rotation substantially perpendicular to a longitudinal axis of the elongate sensor assembly, wherein the axes of rotation of the pairs of wheels of said transportation apparatuses are parallel, and an orientation structure connected to the elongate sensor assembly to prevent relative rotation between the orientation structure and the elongate sensor assembly, the orientation structure comprising at least one radially extending orientation projection, in a transverse outline of the logging tool assembly a said orientation projection extending between the pair of wheels so that the shortest distance between a centre of gravity of the elongate sensor assembly and the wellbore wall is when the pair of wheels of the transportation apparatus are in contact with the wellbore wall.
 2. The assembly of claim 1, wherein there is a single most stable orientation within the wellbore with the logging tool assembly on the wheels of the transportation apparatuses and with the elongate sensor assembly closest to the low side of wellbore wall.
 3. The assembly of claim 1, wherein each wheel has a diameter substantially greater than one of the diameter, width or height of the elongate sensor assembly.
 4. The assembly of claim 1, wherein in a transverse view of the logging tool assembly the elongate sensor assembly is carried between the pair of wheels.
 5. The assembly of claim 1, wherein the elongate sensor assembly comprises a sampling tool oriented to take a sample and/or measurement from a desired side of the wellbore with the logging tool assembly in the stable position.
 6. The assembly of claim 1, wherein the elongate sensor assembly comprises a sampling tool oriented to take a sample and/or measurement from a horizontal side of the wellbore with the logging tool assembly in the stable position.
 7. The assembly of claim 1, wherein the elongate sensor assembly comprises a sampling tool oriented to take a sample and/or measurement from a high-side of the wellbore with the logging tool assembly in the stable position.
 8. The assembly of claim 1, wherein the elongate sensor assembly comprises a sampling tool oriented to take a sample and/or measurement from a low-side of the wellbore with the logging tool assembly in the stable position.
 9. The assembly of claim 1, wherein, in the stable position, the axes of rotation of the wheels of the plurality of sensor transportation devices are above the centre of mass of the elongate sensor assembly with the logging tool assembly in the stable position.
 10. The assembly of claim 1, wherein the axes of rotation of the wheels of the plurality of sensor transportation devices are on or below the centre of mass of the elongate sensor assembly with the logging tool assembly in the stable position.
 11. The assembly of claim 1, wherein the orientation projection is a bow-spring eccentering device.
 12. The assembly of claim 1, wherein the orientation structure comprises a powered orientation projection moveable between an extended or raised position and a retracted or lowered position.
 13. The assembly of claim 1, wherein lateral extremities of the at least one orientation projection and the bottom of the wheels present lateral extremities of the transverse outline of the logging tool assembly.
 14. The assembly of claim 1, wherein lateral extremities of the at least one orientation projection and the top and bottom of the wheels present lateral extremities of the transverse outline of the logging tool assembly.
 15. The assembly of claim 1, wherein the lateral extremities of the transverse outline of the logging tool assembly have a rotational centre that is offset from the centre of mass of the elongate sensor assembly so that the sensor transportation apparatus is oriented in the most stable position with the centre of mass of the elongate sensor assembly below the rotational centre.
 16. The assembly of claim 1, wherein the pair of wheels are integrally formed as a single wheel providing two spaced apart edges to contact the well bore wall.
 17. A logging tool assembly comprising: an elongate sensor assembly, a plurality of sensor transportation apparatuses for transporting the elongate sensor assembly through a wellbore, the sensor transportation apparatuses spaced apart along the elongate sensor assembly, wherein each sensor transportation apparatus comprises: an engagement structure to connect the sensor transportation apparatus to the elongate sensor assembly and prevent relative rotation between the sensor transportation apparatus and the elongate sensor assembly, and one or more pairs of skids arranged parallel to a longitudinal axis of the elongate sensor assembly, and an orientation structure connected to the elongate sensor assembly to prevent relative rotation between the orientation structure and the elongate sensor assembly, the orientation structure comprising at least one radially extending orientation projection, in a transverse outline of the logging tool assembly a said orientation projection extending between the pair of skids so that the shortest distance between a centre of gravity of the elongate sensor assembly and the wellbore wall is when the pair of skids of the transportation apparatus is in contact with the wellbore wall. 